1. Field of the Invention
This invention relates to a process for degassing and filtering liquids and an apparatus for performing the process. In the process, a feed stream of liquid is divided into a process stream that is continuously passed through a main filter to a specific use and a fractional stream that is removed from an area of the main filter and cycled for reuse.
2. Description of the Related Art
Degassing and filtration are particularly suited for the preparation of emulsions, solutions and dispersions used for coating, particularly coating, in the production of photographic film, electronic data media and similar products. Each gas bubble and each foreign particle cause flaws in the final product.
A process and apparatus for degassing and filtration are known from European Patent No. 0,046,919. A cartridge filter, that is, a type of depth filter, serves as the main filter. Its filter element retains foreign particles. Air or gas bubbles collect on the surface of the filter element, coalesce and rise to the upper part of the filter chamber. A backflow line is connected there to forward the fractional stream containing bubbles to a degassing system from which the material can be recycled to production As such filter cartridges have a limited service life, because the filter surface and its pores become gradually clogged by bubbles and particles, a switching device is provided by which a second cartridge filter takes over the function of the first filter cartridge and the latter can be replaced.
Thus, degassing and filtration can be continuous. However, filter behavior changes as a result of retained bubbles and particles. The liquid recycled for use does not always have a constant particle size distribution. This is a disadvantage in many processes, for example, in the production of photographic film.
Continuous cleaning of a filter by backflusing is also known. See U.S. Pat. No. 3,635,348. For this purpose, a rotor is provided on the inlet surface of the filter. The rotor has a radial slot on the inlet surface of the filter and a hollow interior connected to an outlet line. This type of filter is used mainly for handling waste water and other contaminated water, that is, liquids with low viscosity and relatively large contaminating particles.
It is an object of the present invention to provide a process for continuously degassing and filtering a liquid, which process assures not only effective removal of bubbles and solid particles, but also a continuously constant particle size distribution in the liquid delivered to a specific use.